Standard procedures for preparing tissue samples for microscopic examination involve embedding the tissue sample in paraffin and slicing the paraffin-embedded tissue sample very thinly with a microtome. Prior to embedding the tissue sample, the tissue sample is pre-treated in various solutions appropriate to the examination. Typically, prior to paraffin embedding, the tissue sample is fixed, dehydrated, cleared, infiltrated with molten paraffin and, depending on the test, stained. Such prior treatment of the tissue sample requires subjecting the tissue sample to contact with various fluids, including ethanol, xylene, formaldehyde and water.
A histology laboratory processes a large number of tissue samples for examination and it is important that the tissue samples be prepared as efficiently as possible. A large variety of apparatus has been developed to improve the efficiency of the preparation process. For example, U.S. Pat. No. 3,674,396 to McCormick discloses capsules in which a tissue sample is both prepared for embedding through exposure to various solutions and is then embedded in proximity to the capsule. The '396 McCormick patent discloses a process wherein the tissue sample is statically exposed to the various fluids required for preparation of the tissue samples. In the capsules of the '396 McCormick patent, perforated bottom walls are used to retain the tissue samples while providing access to the tissue samples of the various solutions and finally to molten paraffin.
In previous procedures for processing the tissue sample after subjecting the tissue sample to the various fluids required to treat the sample, the treated tissue sample is removed from the capsule or cassette and is placed into the well of a mold. Molten embedding material is then poured over the tissue sample. The cassette used to process the tissue sample is then placed over the well in the mold and additional molten embedding material is poured into the cassette. After the embedding material solidifies, a cast block is formed that includes the capsule as its base and a protruding portion having the tissue specimen disposed adjacent its front surface. In accordance with standard procedure, the size of various cassettes and capsules which have been developed for processing tissue sample, has been relatively standardized so that the cassette or capsule can be used as the chuck in a microtome slicing device.
U.S. Pat. No. 5,080,869 to McCormick describes a particularly useful cassette for processing tissue samples in a highly efficient manner. The cassette of the '869 McCormick patent is stackable and can be used for preparing a plurality of specimens. The cassette generally includes a plurality of apertures disposed in the walls of the cassette for passage of processing fluids in a direction both orthogonal and parallel to the plane of the bottom wall of the cassette. The cassette also includes a sloping extension of the front wall of the cassette for ease in placing indicia on the cassette for identification of the sample.
It would be desirable to provide an embedding mold for use with the cassette of the type disclosed in the '869 McCormick patent which facilitates embedding the processed tissue sample without incurring problems of previous tissue processing capsules and cassettes wherein the capsule or cassette is placed loosely in an embedding mold and movement of the cassette can occur causing wax to overrun the sides of the cassette. Such excess wax must be flash trimmed to conform the shape of the cassette to the chuck of the microtome which holds the cassette and specimen for cutting. Precision casting would save technical time and improve function.
For example, U.S. Pat. Nos. 4,557,903 and 4,569,647, both to McCormick, disclose improved apparatus for preparing and embedding tissue samples for histological examination. In the '903 McCormick patent, a tissue specimen processing capsule is provided which includes a pair of interlocking frames, each of the frames having a porous web spread across its central opening for holding a tissue specimen in a region divided between the webs. The porous webs permit access to the specimen by processing and impregnating fluids. After the tissue specimen is processed, it is removed from the capsule and placed in a depression of a mold. The empty capsule is placed over the mold depression containing the tissue specimen. Molten paraffin is poured into the mold to fill the depression and to cover the tissue specimen and the porous material of the capsule. The molten paraffin solidifies to form a tissue block with the capsule serving as a clampable base for an outwardly extending, tissue-containing portion.
The '647 McCormick patent discloses an improved method for contacting a tissue specimen with a fluid which is used to treat the tissue specimen. In the '647 McCormick patent, capsules for processing and embedding tissue samples each include a mold, which provides a cavity to receive the tissue sample. The mold has an upper end and a porous or non-porous bottom. The capsule further includes a cover which fits over the open upper end of the mold. The cover includes a frame on which is located a web of porous material intermediate the top and bottom of the frame so that the cover is provided with a recess. The porous web provides access to tissue processing liquids and liquid tissue embedding material, such as paraffin, but prevents passage of any small portions of the tissue specimen which may be generated, thereby preventing cross-contamination of individually capsuled and jointly processed tissue samples. After the tissue samples have been treated with the required fluids, the cover recess above the porous web is at least partially filled with molten paraffin embedding material so that when the embedding material solidifies, the porous web is embedded and the solidified material is thereby formed into a block in the mold. With the porous web and the tissue sample mutually embedded in the block of solidified paraffin, the block is removed from the mold and the cover may be clamped in a microtome and sliced by a microtome blade.
While apparatus and methods for preparing and embedding tissue samples for histological examination have progressed over the years to provide more efficiency in the preparation of tissue specimen, the large number of tissue samples which are prepared daily by histological laboratories, require the most efficient techniques available to increase the number of samples that can be processed and to reduce the cost of such processing.
Accordingly, it is the principal object of the present invention to provide apparatus for use in embedding tissue specimen for histological examination which increases the efficiency of the embedding operation of a specimen and which reduces the cost of preparing tissue samples for microtome slicing and treatment.
Another object of the present invention is to provide an embedding mold for utilization with a cassette to operate in cooperation with such cassette to provide an improved embedding technique.
These and other objects of the invention will become more apparent from the following detailed description and the accompanying drawings.